An optical device which controls the transmittance (or reflectance) of incident light needs a high contrast ratio and a high efficiency of light utilization.
One well-known optical device for controlling transmittance of light with voltage application is the liquid crystal panel. A liquid crystal panel includes a pair of substrates and a liquid crystal layer which is provided between these substrates. In a liquid crystal panel, liquid crystal molecules within the liquid crystal layer undergo changes in their alignment depending on the level of voltage being applied across the liquid crystal layer, which results in changes in the transmittance of light entering the liquid crystal panel. Liquid crystal panels have a very high contrast ratio, and therefore are widely used in display devices.
However, many liquid crystal panels are of the type that employs polarizers; therefore, half or more of the light which is utilized for displaying is absorbed at the polarizers. This results in a low efficiency of light utilization. Accordingly, development of optical devices which do not require polarizers has been under way in the recent years.
Non-Patent Document 1 proposes a display cell which does not require polarizers. The display cell disclosed in Non-Patent Document 1 has a construction where a host fluid (medium) and polymer (resin-coated) flakes dispersed within the medium are interposed between a pair of electrodes. By applying an electric field between the pair of electrodes, the alignment directions of the polymer flakes are changed, thereby altering the optical characteristics (light reflectance) of the display cell. As a specific example of the medium, Non-Patent Document 1 discloses propylene carbonate and epoxy-terminated polydimethylsiloxane (DMS-E09).
Patent Document 1 discloses an optical device including a suspension layer which contains polymer flakes. In this optical device, the polymer flakes can be rotated with application of an electric field to the suspension layer, whereby the optical characteristics of the suspension layer are altered.
The display cell of Non-Patent Document 1 and the optical device of Patent Document 1 mentioned above do not require polarizers, and therefore can attain a higher efficiency of light utilization than that of a liquid crystal panel.